Research On High-Sensitivity Acquisition Algorithm For BD Signal

Bei Dou Navigation Satellite System is a global navigation satellite system which is developed and constructed independently by China.Now BD chip is used more and more frequently by personal handheld and automotive equipment with the development of technology.When the user is in a harsh environment,due to object occlusion,multipath interference and noise,the satellite signal strength will be seriously attenuated.Resulting in the inability to reach the minimum power requirement for the normal acquisition.Although the accumulation of satellite signal energy can be done by extending the integration time,it is impossible to calculate integral of the BD B1 I signal in a long time due to the structure of the D1 and D2 navigation message which leads to high rate bit transition.So this presents a huge challenge in B1 I signal acquisition.This thesis researches on the high sensitivity acquisition algorithm of BD B1 I signal and the performance of the algorithm which is optimized by bit correction,optimal edge determination and symbol combination.Aiming at the problem of high bit transition caused by secondary code modulation,this thesis provides an improved bit transition correction method.The algorithm can effectively control the gain loss caused by the inversion of the symbol through inverting the compensation of the navigation data within 1ms and combining the improved differential coherence integration method to extend the total integration time which can accumulate the signal energy.At the same time,on the basis of the bit transition correction,the weighted superposition of the integral result is carried out by using the characteristic sequence of the secondary coding structure,which not only can control the noise loss and increase the output gain,but also determine the secondary coding sequence's phase value in a short time.Besides,an improved non-coherent combination method is proposed for the B1 I signal which is modulated with D2 navigation message.This method uses the data shift to determine the starting edge of the navigation data in a short time,and the correlation result of the data in the adjacent information bits can be combined together by the best symbol combination to reduce the square loss problem in the non-coherent combination method.Simulation experiments were carried out by local simulation signal and the real BD B1 I signal.The simulation results show that the above optimization algorithm can effectively control the gain loss caused by bit transition and reduce the noise power to improve the output signal-to-noise ratio.